Target Sensitivity To Organophosphorous Insecticides And CYP450-mediated Desulfurization In Fish

This reseach assayed target sensitivity of fish to organophosphorous insecticides and CYP450-mediated desulfurization of them. Four species of fish, namely swordtail fish Xiphophorus helleri, zebrafish Brachydanio rerio, topmouth gudgeon Pseudorasbora parva, and sunfish Leponus macrohirus, and three types of organophosphorous insecticides, including parathion, malathion, and chlorpyrifos, were involved in the study.To evaluate the sensitivity of target enzyme, the bimolecular reaction constants (Ki) of brain AChE for paraoxon-ethyl, malaoxon, and chlorpyrifos-oxon were calculated in vitro. Results showed that for paraoxon-ethyl, the sensitivity of brain AChE was in order of swordtail fish>topmouth gudgeon>zebrafish and sunfish (p<0.05). For malaoxon, it was in order of sunfish>swordtail fish>topmouth gudgeon and zebrafish (p<0.05). For chlorpyrifos-oxon, it was in order of swordtail fish>sunfish and topmouth gudgeon>zebrafish (p<0.05).Relative rates of production of active metabolites of the insecticides were scaled in vitro by rates of inhibition of endogenous acetylcholinesterase (AChE) by the metabolites. Result of the liver study appeared that for parathion, species order concerning the affinity is swordtail fish and sunfish>zebrafish and topmouth gudgeon (p<0.05). For malathion sunfish had a significantly higher affinity than swordtail fish, zebrafish and sunfish (p<0.05). For chlorpyrifos, species order concerning the affinity was topmouth gudgeon, zebrafish, sunfish, wordtail fish, while the difference between topmouth gudgeon and swordtail fish were significant (p<0.05). Result of the brain experiment indicted that for parathion, there were no significant differences between 4 species fish. (p>0.05). For malathion, species order concerning the affinity was topmouth gudgeon, zebrafish, sunfish, wordtail fish, while the difference between topmouth gudgeon and swordtail fish were significant (p<0.05). For chlorpyrifos, species order concerning the affinity was topmouth gudgeon, sunfish>zebrafish, swordtail fish (p<0.05). In summary, the result confirmed the differences both in CYP450 desulfurization activity and in target enzyme sensitivity to organophosphorous insecticides in fish.